The present invention relates to microtransformers and, more particularly, to a programmable microtransformer design incorporating flat-wire windings embedded in a thin-film substrate, the secondary windings having multiple tap points connected to digital controls that permit dynamic adjustment of the turns ratio. The microtransformer layout is scalable based on the relative size of the circuit card on which it resides.
Electrical transformers are commonly implemented as discrete analog components. Most transformers are manufactured using an iron-based core material wrapped with wire windings, but this configuration increases their mass, volume and cost. Traditional fabrication methods preclude the use of common transformers as embedded systems (part of a larger overall system or product) because space confines require more versatile components. However, there are efforts directed toward developing thin-film transformers including Micro-Electro-Mechanical or “MEMS”-based transformers.
For example, US Patent Application 20050062575 by Gardner shows an integrated MEMS-based transformer in which coil windings are deposited on a substrate, and magnetic core material is included as interspersed layers between windings and dielectrics. The effective turns ratio of the Gardner construct depends on different material substrates, as well as the substrate layer thickness between windings.
U.S. Pat. No. 6,707,367 to Castaneda et al. shows an overlay transformer with flat wire coils on a substrate, primary on one side and secondary on the other. The secondary coils are tapped, and intermediate dielectric layers are incorporated. This disclosure is sharply limited to a specific octagonal geometry with two (“first” and “second”) windings and no magnetic core material. The construction is based on traditional printed circuit manufacturing technology. Further, the inter-winding substrate thickness is assumed.
US Patent Application 20020130753 to Merriam uses multiple layers of non-conductive material with individual coil traces stacked to form a multi-turn transformer. Merriam also notes that transformers frequently provide variable voltage output and suggests a center tap layer. However, there is only one winding per layer, and ceramic substrate layers are used. The ceramic influences the effective turns ratio based on dielectric variance of the ceramic. In addition, a multi-layer ceramic (MLCC) method of building inductive elements is inferred, not a printed circuit board assembly process.
U.S. Patent Application No. 20040070893 to Ahn et al. shows a microtransformer for a high-performance system-on-chip power supply application-specific to a DC-DC converter. The coils are fabricated by patterned deposition on both sides of a substrate (the hallmark of a traditional printed circuit process). Multiple tap implementations are suggested.
U.S. Pat. No. 6,580,334 to Simburger et al. issued Jun. 17, 2003 shows a monolithically integrated transformer using slotted windings produced by silicon bipolar technology with three metallic layers. This patent states that “the absolute size of the transformer is virtually unimportant, but merely determines the frequency range of the optimum function or the inherent resonant frequencies. The diameter of an optimum transformer for frequencies from 800 to 900 MHz is, for example, about 400 um.” (Column 4, Lines 8-12). However, this description is somewhat a misnomer, because to obtain a desired frequency and resonance response (even a desired power rating) the geometric physicality of the inductive element(s) constructed (i.e., ‘absolute size’) directly determines its claims and intended application, as does the circuit elements tied to it.
In summary of the above-described and other related art, these technologies intrinsically show that the desired performance depends on 1) microtransformer geometry; 2) construction methods; and 3) actual composition of matter used in making these types of devices (substitutions of materials in this area is not an obvious matter of design choice). Indeed, some of the foregoing examples simply cannot be built effectively using printed circuit board fabrication techniques because they require vertical angled traces (connecting layer-to-layer), and cannot be done without drilling a hole through the board.
The existing microtransformers have a second limitation in that their turns ratios are typically fixed, and it is difficult to dynamically configure and control the turns ratio. There is a second line of research directed toward varying the effective turns ratio using switched secondary taps.
For example, U.S. Pat. No. 6,417,651 to Kronberg, U.S. Pat. No. 5,969,511 to Asselman et al., and US Patent Application No. 20040100341 by Luetzelschwab et al. all use MEMs-switches to tune a high power transformer by selecting secondary winding taps. They provide a means of electronic switching using either SCR banks (Asselman) or digitally-controlled switches (Kronberg). However, they employ a multiplicity of discrete elements dedicated to high-energy power applications far in excess of the compact constructions envisioned by the present inventors.
U.S. Pat. No. 6,232,841 to Bartlett et al. issued May 15, 2001 shows an integrated tunable high efficiency power amplifier made from micro-electromechanical MEMs devices capable of being integrated with the control circuitry needed to produce the control signals and other amplifier components on a common substrate. The Bartlett U.S. Pat. No. 6,232,841 does combine an overlay transformer with an on-board switching network and a center-tapped transformer, but not multi-taps or layered coils.
Therefore, there remains a need for a programmable microtransformer design better-suited for MEMS-based manufacture and subsequent use in embedded systems that incorporate flat-wire windings embedded in a layered thin-film substrate, the secondary windings having multiple tap points connected to digital controls that permit dynamic adjustment of the turns ratio.
In all, the foregoing related art examples, size, frequency characteristics and energy capacity concerns drive the design variables, and so the stated goals implemented in a compact packaging of circuitry for a specific power load requires an entirely new set of geometries, materials and assembly.